Field
The disclosed concept pertains generally to circuit breakers used in power transmission and distribution systems, and, more particularly, to a portable diagnostic apparatus including an onboard diagnostic feature for performing diagnostic testing on circuit breakers, such as, without limitation, low or high voltage power circuit breakers.
Background Information
Electrical power transmission and distribution systems typically utilize a plurality of power circuit breakers which include one or more sets of separable contacts for protecting circuits against overcurrent conditions. In the field, a number of such circuit breakers are generally mounted and housed within a non-conductive housing or enclosure, often referred to as a switchgear enclosure. Power connections for the circuit breakers are generally terminated in the rear of the enclosure, and instrumentation and control terminal blocks for the circuit breakers may either be mounted in the rear or the front of the enclosure. In many cases, switchgear equipment as just described is provided in a drawout configuration wherein the circuit breakers may be completely removed from the front of the switchgear enclosure for repair, testing or maintenance. On other cases, the circuit breakers are mounted on customized framework, generally called a fixed breaker, and may not be able to racked out of the framework.
The electrical power transmission and distribution industry has a huge installed-base of power circuit breakers. Many of the circuit breakers have been in the field for a long time and are still completely operational. These older circuit breakers, unlike many more modern circuit breakers, do not have any built-in diagnostic sensors for monitoring the operation thereof. If such a circuit breaker fails, the customer typically immediately replaces the failed circuit breaker with a spare circuit breaker available on site, and transfers the failed circuit breaker to a remote maintenance site for diagnostic testing and repair.
Many of the circuit breakers in the electrical power and distribution industry are what are known as drawout circuit breakers. Drawout circuit breakers often include a mechanism for moving the breaker in and connecting the breaker to corresponding electrical contacts, a location known as the “racked-in” position. When in the racked-in position, the circuit breaker is coupled to the main electrical circuit and provides the interruption functionality for which it is intended. If the drawout mechanism is activated to the “racked-out” position, the circuit breaker is disconnected from the electrical contacts and the main electrical circuit. The circuit breaker may be moved to the racked-out position, for example, when maintenance is performed on the main electrical circuit. Typical racking mechanisms often include a third or “test” position in between the “racked in” or “Connected” position and “Racked out” or “Disconnected” position. In the test position the circuit breaker can be closed, opened or tripped in order to check the functionality of the circuit breaker by evaluating proper operation of the internal and external accessories such as auxiliary switches, shunt trip and under voltage and secondary circuits.
Diagnostic testing and repair at such a remote maintenance site often makes the diagnosis of the real problem more difficult, since the circuit breaker will often have to be tested without electrical control power due to the unavailability of a proper fixture such as switchgear enclosure, testing cabinet, etc. In addition, on-call service Engineers or maintenance staff at the customer's site may face problems understanding the breaker mechanism and may not be able to repair the issue due to lack of knowledge and/or sensor diagnostic data. Thus, there is a need for a diagnostic device that can easily and readily interact with the circuit breaker, under drawout or fixed configurations, as discussed above, and provide onboard diagnostic information. In the case of a drawout breaker, it is also often necessary to analyze the breaker functioning under switchgear control signals, giving rise to at least three modes of diagnostic protocol, including, but not limited to, ONLINE mode, Semi-Online mode and Offline mode.
Further, the time constrains at maintenance shops due to the cost associated with the downtime or maintenance itself are critical. This creates a need for quick guidance as to the appropriate and accurate repair instructions further to the on board diagnostic indications. This is needed to further improve the service efficiency for the breaker failure event. This requires an automated diagnostic and repair methodology to be implemented in the new portable device that can be used at the customer's site.